Silicon-based negative electrode and preparation method therefor, and battery

Abstract

A preparation method for a silicon-based negative electrode, comprising: obtaining a covalent organic framework material precursor; performing a first mixing of the covalent organic framework material precursor and silicon nanosheets to obtain a mixed solution; and heat-treating the mixed solution to cause a polymerization reaction of the covalent organic framework material precursor, generating a covalent organic framework material buffer layer, and causing the covalent organic framework material buffer layer to adhere to at least part of the surface of the silicon nanosheets, so as to obtain a silicon-based negative electrode.

Description

A silicon-based anode and its preparation method and battery

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application No. 202411630949.X, filed on November 15, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of silicon-based anode technology, and in particular to a silicon-based anode, its preparation method, and a battery. Background Technology

[0004] With the rapid development of the new energy industry, the range anxiety and safety anxiety of electric vehicles are becoming increasingly prominent. Solid-state batteries, due to their high energy density and high safety, have become an important way to solve these two major anxieties of new energy vehicles. In order to significantly improve the energy density of solid-state batteries, high-capacity material systems are often used for the positive and negative electrodes. Typically, a silicon-based negative electrode made of graphite and silicon materials is combined with a high-nickel ternary electrode to form a solid-state battery.

[0005] Although silicon-based anodes have high specific capacity, their high expansion rate can lead to problems such as particle pulverization, electrode structure damage, and repeated growth of the solid electrolyte interphase (SEI) layer, which affect the various electrochemical performances of the battery. Summary of the Invention

[0006] This disclosure provides a silicon-based anode, a method for its fabrication, and a battery, thereby solving the technical problem of how to reduce the expansion rate of the silicon-based anode.

[0007] Firstly, this disclosure provides a method for preparing a silicon-based anode, comprising: obtaining a covalent organic framework material precursor; mixing the covalent organic framework material precursor with silicon nanosheets to obtain a mixed solution; and subjecting the mixed solution to heat treatment to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and attaching the covalent organic framework material buffer layer to at least a portion of the surface of the silicon nanosheets to obtain a silicon-based anode.

[0008] Secondly, this disclosure provides a silicon-based anode prepared by the method described in any one of the first aspects.

[0009] Thirdly, this disclosure provides a battery including the silicon-based negative electrode as described in any one of the second aspects. Attached Figure Description

[0010] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0011] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0012] Figure 1 shows a schematic flowchart of a method for preparing a silicon-based anode according to some embodiments of the present disclosure.

[0013] Figure 2 shows a schematic diagram of the reaction in a method for preparing a silicon-based anode according to some embodiments of the present disclosure. Embodiments of the present invention

[0014] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0015] Various embodiments of this disclosure may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0016] In this disclosure, unless otherwise stated, directional terms such as “upper” and “lower” specifically refer to the orientation in the accompanying drawings. Furthermore, in the description of this disclosure, terms such as “comprising” and “including” mean “including, but not limited to”. In this document, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, “at least one” means one or more, and “more than one” means two or more. “At least one,” “at least one of the following,” or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, “at least one of a, b, or c,” or “at least one of a, b, and c,” can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple. In the proportional relationships discussed in this article, the parameters that need to be described by proportion should be understood as the first term of the proportion in the order of description, while the proportion figures should be understood as the second term of the proportion. For example, if the molar ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one-to-one with the proportion figures in the proportion in the order of description, that is, moles of substance A : moles of substance B : moles of substance C = 1 : 2 : 3.

[0017] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this disclosure are available on the market or can be prepared by existing methods.

[0018] In a first aspect, this disclosure provides a method for preparing a silicon-based anode. Figure 1 shows a schematic flowchart of a method for preparing a silicon-based anode according to some embodiments of this disclosure. Referring to Figure 1, the method for preparing the silicon-based anode includes:

[0019] S1. Obtain the precursor of the covalent organic framework material;

[0020] S2. The covalent organic framework material precursor is first mixed with silicon nanosheets to obtain a mixed solution; and,

[0021] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0022] In some embodiments, a covalent organic framework material precursor is obtained, comprising:

[0023] Tris(4-aminophenyl)amine, diacid monomer, and solvent were mixed in a second step to obtain a precursor for a covalent organic framework material.

[0024] In the embodiments disclosed above, tris(4-aminophenyl)amine (TAPA) has a stable molecular structure, and the diacid monomer serves as the conjugate anhydride. By dissolving tris(4-aminophenyl)amine and the diacid monomer in a solvent, a polymerization reaction can occur between the tris(4-aminophenyl)amine and the diacid monomer during heat treatment to obtain a covalent organic framework material with a stable structure. Covalent organic framework materials are a new type of crystalline porous polymer material composed of organic molecules linked by covalent bonds. These materials possess characteristics such as high chemical stability, high thermal stability, structural diversity, designability, and a regular pore structure. Therefore, during the heat treatment of the mixed solution, tris(4-aminophenyl)amine and the diacid monomer undergo a polymerization reaction on the surface of silicon nanosheets to generate a covalent organic framework material. This covalent organic framework material forms a buffer layer in situ and adheres to at least a portion of the surface of the silicon nanosheets. This buffer layer plays a positive role in suppressing and buffering the large volume changes caused by the charging and discharging of the silicon nanosheets. The covalent organic framework material buffer layer obtained by the polymerization reaction of the precursor of the covalent organic framework material does not contain any metal elements. The raw materials used in the synthesis are all common organic raw materials, which have the advantages of wide availability, no pollution and low cost.

[0025] In some embodiments, the dihydric anhydride monomer includes at least one of the following: pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, and perylenetetracarboxylic dianhydride.

[0026] In the above embodiments of this disclosure, the dihydric anhydride monomer can be one or more of pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, and perylenetetracarboxylic dianhydride, wherein pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, and perylenetetracarboxylic dianhydride are all conjugated anhydrides. The dihydric anhydride monomer composed of one or more of these conjugated anhydrides has conjugated properties, thereby enabling it to undergo a polymerization reaction with tris(4-aminophenyl)amine to form a covalent organic framework material buffer layer with a stable structure.

[0027] In some embodiments, the molar ratio of tris(4-aminophenyl)amine to the diacid monomer is (3:2) to (4:2).

[0028] In the embodiments disclosed above, the molar ratio of tris(4-aminophenyl)amine to the diacid monomer can be (3:2) to (4:2), thereby causing the tris(4-aminophenyl)amine and the diacid monomer to undergo a polymerization reaction to form a stable covalent organic framework material buffer layer. For example, the molar ratio of tris(4-aminophenyl)amine to the diacid monomer can be 3:2, 4:2, 4:3, etc.

[0029] In some embodiments, the molar ratio of the above-mentioned tris(4-aminophenyl)amine to the diacid monomer can be 3:2.

[0030] In some embodiments, the solvent is an amide solvent.

[0031] In the embodiments described above, the solvent can be an amide solvent, which has good solubility and thermal stability, thereby achieving the purpose of fully dissolving tris(4-aminophenyl)amine and diacid monomers. For example, the amide solvent can be one or a combination of N-N'-dimethylacetamide (DMF) and N-N'-dimethylformamide.

[0032] In some embodiments, the volume of solvent is 150 mL to 250 mL relative to 1 mol of diacid monomer.

[0033] In this embodiment, the volume of solvent can be 150 mL to 250 mL relative to 1 mol of diacid monomer, thereby maintaining the tris(4-aminophenyl)amine and diacid monomer in the covalent organic framework precursor within a suitable concentration range, thus ensuring that the subsequent polymerization reaction yields an ideal covalent organic framework buffer layer. If the amount of solvent is too large and exceeds 250 mL, it will to some extent lead to a low concentration of tris(4-aminophenyl)amine and diacid monomer in the covalent organic framework precursor, resulting in prolonged polymerization time and incomplete reaction. If the amount of solvent is too small and below 150 mL, it will to some extent lead to a high concentration of tris(4-aminophenyl)amine and diacid monomer in the covalent organic framework precursor, resulting in an excessively fast polymerization rate, ultimately making it difficult for the polymerization reaction to generate a uniform covalent organic framework buffer layer and for it to adhere to the surface of silicon nanosheets. For example, the volume of solvent relative to 1 mol of diacid monomer can be 150 mL, 160 mL, 170 mL, 180 mL, 190 mL, 200 mL, 210 mL, 220 mL, 230 mL, 240 mL, 250 mL, etc.

[0034] In some embodiments, the molar ratio of silicon atoms to diacid monomers in silicon nanosheets is (20:1) to (40:1).

[0035] In this embodiment, the aforementioned covalent organic framework material buffer layer can suppress and buffer the large volume changes caused by silicon nanosheets during charging and discharging. The molar ratio of silicon atoms to diacid monomers in the silicon nanosheets can be (20:1) to (40:1), thereby maintaining a balance between the silicon content and the content of the covalent organic framework material buffer layer in the silicon-based anode, thus fully suppressing and buffering the large volume changes caused by silicon nanosheets during charging and discharging. If the molar ratio of silicon atoms to diacid monomers in the silicon nanosheets is higher than 40:1, it will lead to a lower amount of covalent organic framework material generated to a certain extent, resulting in less covalent organic framework material buffer layer attached to the surface of the silicon nanosheets, making it difficult to exert the inhibitory effect of the covalent organic framework material buffer layer on the expansion of silicon nanosheets; if the molar ratio of silicon atoms to diacid monomers in the silicon nanosheets is lower than 20:1, it will lead to a lower silicon content in the silicon-based anode to a certain extent, resulting in a significant reduction in the reversible capacity of the silicon-based anode. For example, the molar ratio of the silicon nanosheets to the diacid monomer can be 20:1, 25:1, 30:1, 35:1, 40:1, etc. Optionally, the silicon nanosheets used in the embodiments of this disclosure are pure silicon nanosheets, that is, silicon nanosheets containing only silicon atoms. Optionally, the size of the silicon nanosheets can be 100 nm to 500 nm.

[0036] Covalent organic framework (COB) buffer layers exhibit high chemical stability and elasticity. Under pressure, the polymer chains within the COB buffer layer do not break, and the layer returns to its original shape after the pressure is removed. Silicon nanosheets are low-cost and have high reversible capacity, but their high expansion rate significantly limits their industrial application in silicon-based anodes and batteries. In the above embodiments of this disclosure, a covalent organic framework material buffer layer is constructed in situ on the surface of silicon nanosheets, thereby binding the silicon nanosheets within the covalent organic framework material buffer layer. Specifically, the covalent organic framework material precursor undergoes a polymerization reaction during heat treatment to generate the covalent organic framework material buffer layer. This covalent organic framework material buffer layer is attached to at least a portion of the surface of the silicon nanosheets. The covalent organic framework material buffer layer and the silicon nanosheets are composited during heat treatment, ultimately resulting in a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of the silicon nanosheets. This means that the surface of the silicon nanosheets has a covalent organic framework material buffer layer. When the silicon nanosheets expand, the covalent organic framework material buffer layer will at least absorb some of the expansion stress of the silicon nanosheets. Although the covalent organic framework material buffer layer will expand slightly along with the silicon nanosheets, the expansion rate will not be as large as when the silicon nanosheets expand alone. Thus, the covalent organic framework material buffer layer plays a certain binding role on the silicon nanosheets. When the silicon nanosheets shrink, the covalent organic framework material buffer layer also shrinks synchronously and returns to its original state. Therefore, the strong confinement and buffering effect of the covalent organic framework material buffer layer can effectively suppress and buffer the huge volume changes caused by silicon nanosheets during charging and discharging, thus reducing the expansion rate of silicon-based anodes. Consequently, covering the surface of silicon nanosheets with a covalent organic framework material buffer layer can effectively solve the problem of high expansion rate of silicon nanosheets, thereby improving the industrial application of silicon nanosheets in silicon-based anodes and batteries.

[0037] For example, Figure 2 shows a schematic diagram of the reaction in a method for preparing a silicon-based anode according to some embodiments of the present disclosure. Referring to Figure 2, a mixed solution containing pyromellitic dianhydride, TAPA, and silicon nanosheets is heated. The pyromellitic dianhydride and TAPA can undergo a polymerization reaction to obtain a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer can be uniformly attached to the surface of the silicon nanosheets, resulting in a silicon-based anode with a covalent organic framework material buffer layer uniformly attached to the surface of the silicon nanosheets.

[0038] In some embodiments, the process parameters for heat treatment include: a heating temperature of 120°C to 180°C and a heating time of 56 h to 80 h.

[0039] In the embodiments disclosed above, a covalent organic framework material buffer layer is generated by heat treatment to polymerize tris(4-aminophenyl)amine and diacid monomers. This covalent organic framework material buffer layer is attached to the surface of the silicon nanosheets, thus at least partially coating the surface of the silicon nanosheets with the covalent organic framework material buffer layer. This buffer layer can constrain the expansion of the silicon nanosheets, forming a constrained sandwich-type silicon-based anode. The heat treatment process parameters include a heating temperature of 120°C to 180°C and a heating time of 56 h to 80 h, which allows sufficient polymerization of tris(4-aminophenyl)amine and diacid monomers, maintaining a suitable polymerization rate to obtain an ideal covalent organic framework material and form a uniform covalent organic framework material buffer layer on the surface of the silicon nanosheets. If the heating temperature is too high or the heating time is too long, the polymerization reaction rate will be too fast, making it difficult to form a uniform covalent organic framework buffer layer on the surface of silicon nanosheets. If the heating temperature is too low or the heating time is too short, it will be difficult for tris(4-aminophenyl)amine to polymerize with the dianhydride monomer or for the polymerization reaction to proceed fully. For example, the heating temperature can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, etc., and the heating time can be 56 h, 60 h, 65 h, 70 h, 75 h, 80 h, etc.

[0040] Secondly, this disclosure provides a silicon-based anode prepared by any of the methods described in the first aspect.

[0041] In the above embodiments of this disclosure, the silicon-based anode prepared by the above-described method for preparing silicon-based anodes has a strong confinement and buffering effect of the covalent organic framework material buffer layer, which can fully suppress and buffer the huge volume change caused by silicon nanosheets during charging and discharging, that is, greatly reduce the expansion rate of the silicon-based anode, thereby preventing the silicon nanosheets from pulverizing, structurally damaging, or other phenomena caused by stress due to excessive expansion during cycling, and improving its cycling stability.

[0042] The silicon-based anode is realized based on the above-described method for preparing silicon-based anodes. The specific steps of the method for preparing silicon-based anodes can be referred to in the above embodiments. Since the silicon-based anode adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0043] Thirdly, this disclosure provides a battery comprising the silicon-based negative electrode as described in any of the second aspects.

[0044] In the embodiments disclosed above, the strong confinement and buffering effect of the covalent organic framework material buffer layer in the silicon-based anode can effectively suppress and buffer the huge volume changes caused by silicon nanosheets during charging and discharging, that is, greatly reduce the expansion rate of the silicon-based anode, thereby preventing the silicon nanosheets from pulverizing or structurally damaging due to stress caused by excessive expansion during cycling, and improving its cycle stability. When this silicon-based anode is applied in a battery, it can reduce electrolyte consumption and promote the formation of a uniform, stable, and robust SEI film (solid electrolyte layer), thereby improving the long-cycle and rate performance of the battery cell. Furthermore, the covalent organic framework material buffer layer on the surface of the silicon nanosheets also plays an auxiliary bonding role; the organic groups abundant on the framework make it easier to combine with the binder, and the covalent organic framework material buffer layer also has lithium storage performance, without significantly reducing battery capacity, making it particularly suitable for lithium-ion batteries.

[0045] The battery is based on the aforementioned silicon-based anode. The specific preparation method of the silicon-based anode can be referred to the above embodiments. Since the battery adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0046] The present disclosure is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0047] Example 1

[0048] S1. Obtain the precursor of the covalent organic framework material.

[0049] Specifically, TAPA and pyromellitic dianhydride are dissolved in DMF. The molar ratio of TAPA to pyromellitic dianhydride is 3:2, and each mole of pyromellitic dianhydride is dissolved in 200 mL of DMF.

[0050] S2. The covalent organic framework material precursor is mixed with silicon nanosheets to obtain a mixed solution.

[0051] Specifically, silicon nanosheets with an average size of 200 nm were uniformly dispersed in the aforementioned covalent organic framework material precursor by ultrasonic dispersion to obtain a mixed solution. The molar ratio of silicon atoms to pyromellitic dianhydride in the silicon nanosheets was 20:1, the ultrasonic dispersion power was 500 W, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 30 min.

[0052] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0053] Specifically, the mixed solution is heat-treated at a heating temperature of 130°C for 64 hours to obtain a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of silicon nanosheets. This silicon-based anode is dispersed in the mixed solution.

[0054] In addition, the mixed solution containing silicon-based anodes after heat treatment is centrifuged, and the separated solids are washed with DMF and ethanol in sequence to obtain silicon-based anode products.

[0055] Example 2

[0056] S1. Obtain the precursor of the covalent organic framework material.

[0057] Specifically, TAPA and naphthalenetetracarboxylic dianhydride are dissolved in DMF. The molar ratio of TAPA to naphthalenetetracarboxylic dianhydride is 3:2, and each mole of naphthalenetetracarboxylic dianhydride is dissolved in 200 mL of DMF.

[0058] S2. The covalent organic framework material precursor is mixed with silicon nanosheets to obtain a mixed solution.

[0059] Specifically, silicon nanosheets with an average size of 200 nm were uniformly dispersed in the aforementioned covalent organic framework precursor by ultrasonic dispersion to obtain a mixed solution. The molar ratio of silicon atoms to naphthalenetetracarboxylic dianhydride in the silicon nanosheets was 20:1, the ultrasonic dispersion power was 500 W, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 30 min.

[0060] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0061] Specifically, the mixed solution is heat-treated at a heating temperature of 130°C for 64 hours to obtain a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of silicon nanosheets. This silicon-based anode is dispersed in the mixed solution.

[0062] In addition, the mixed solution containing silicon-based anodes after heat treatment is centrifuged, and the separated solids are washed with DMF and ethanol in sequence to obtain silicon-based anode products.

[0063] Example 3

[0064] S1. Obtain the precursor of the covalent organic framework material.

[0065] Specifically, TAPA and perylene dianhydride are dissolved in DMF. The molar ratio of TAPA to perylene dianhydride is 3:2, and each mole of perylene dianhydride is dissolved in 200 mL of DMF.

[0066] S2. The covalent organic framework material precursor is mixed with silicon nanosheets to obtain a mixed solution.

[0067] Specifically, silicon nanosheets with an average size of 200 nm were uniformly dispersed in the aforementioned covalent organic framework precursor by ultrasonic dispersion to obtain a mixed solution. The molar ratio of silicon nanosheets to perylene dianhydride was 20:1, the ultrasonic dispersion power was 500 W, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 30 min.

[0068] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0069] Specifically, the mixed solution is heat-treated at a heating temperature of 130°C for 64 hours to obtain a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of silicon nanosheets. This silicon-based anode is dispersed in the mixed solution.

[0070] In addition, the mixed solution containing silicon-based anodes after heat treatment is centrifuged, and the separated solids are washed with DMF and ethanol in sequence to obtain silicon-based anode products.

[0071] Example 4

[0072] S1. Obtain the precursor of the covalent organic framework material.

[0073] Specifically, TAPA and pyromellitic dianhydride are dissolved in DMF. The molar ratio of TAPA to pyromellitic dianhydride is 4:2, and each mole of pyromellitic dianhydride is dissolved in 200 mL of DMF.

[0074] S2. The covalent organic framework material precursor is mixed with silicon nanosheets to obtain a mixed solution.

[0075] Specifically, silicon nanosheets with an average size of 200 nm were uniformly dispersed in the aforementioned covalent organic framework material precursor by ultrasonic dispersion to obtain a mixed solution. The molar ratio of silicon atoms to pyromellitic dianhydride in the silicon nanosheets was 20:1, the ultrasonic dispersion power was 500 W, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 30 min.

[0076] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0077] Specifically, the mixed solution is heat-treated at a heating temperature of 130°C for 64 hours to obtain a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of silicon nanosheets. This silicon-based anode is dispersed in the mixed solution.

[0078] In addition, the mixed solution containing silicon-based anodes after heat treatment is centrifuged, and the separated solids are washed with DMF and ethanol in sequence to obtain silicon-based anode products.

[0079] Example 5

[0080] S1. Obtain the precursor of the covalent organic framework material.

[0081] Specifically, TAPA and pyromellitic dianhydride are dissolved in DMF. The molar ratio of TAPA to pyromellitic dianhydride is 3:2, and each mole of pyromellitic dianhydride is dissolved in 200 mL of DMF.

[0082] S2. The covalent organic framework material precursor is mixed with silicon nanosheets to obtain a mixed solution.

[0083] Specifically, silicon nanosheets with an average size of 200 nm were uniformly dispersed in the aforementioned covalent organic framework precursor by ultrasonic dispersion to obtain a mixed solution. The molar ratio of silicon atoms to pyromellitic dianhydride in the silicon nanosheets was 20:1, the ultrasonic dispersion power was 500 W, the ultrasonic dispersion frequency was 40 kHz, and the ultrasonic dispersion time was 30 min.

[0084] S3. The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least part of the surface of the silicon nanosheet to obtain a silicon-based anode.

[0085] Specifically, the mixed solution is heat-treated at a heating temperature of 170°C for 72 h to obtain a sandwich-type silicon-based anode with a covalent organic framework material buffer layer on the surface of silicon nanosheets. The silicon-based anode is dispersed in the mixed solution.

[0086] In addition, the mixed solution containing silicon-based anodes after heat treatment is centrifuged, and the separated solids are washed with DMF and ethanol in sequence to obtain silicon-based anode products.

[0087] Comparative Example 1

[0088] Silicon nanosheets are used as silicon-based anodes.

[0089] The silicon-based anodes obtained in Examples 1-5 and Comparative Example 1 were used to prepare coin cells. Half-cell tests were performed on the coin cells corresponding to Examples 1-5 and Comparative Example 1, and the test results are shown in Table 1.

[0090] Table 1 Half-cell test results

[0091]

[0092] As shown in Table 1, the covalent organic framework material buffer layer has certain lithium storage performance and does not significantly reduce the battery capacity. The initial capacity of the coin cells in Examples 1-5 is not significantly different from that of the coin cell in Comparative Example 1. After 100 cycles, the capacity of the coin cells in Examples 1-5 remains above 60%, while the capacity of the coin cell in Comparative Example 1 decreases significantly to 15.6%. It is evident that the strong confinement and buffering effect of the covalent organic framework material buffer layer in the silicon-based anode can effectively suppress and buffer the huge volume change caused by silicon nanosheets during charging and discharging, that is, greatly reduce the expansion rate of the silicon-based anode. This allows the silicon nanosheets to maintain a low volume change rate during cycling, preventing pulverization and structural damage caused by stress from excessive expansion, thus improving its cycle stability and significantly increasing the cycle life of the silicon-based anode.

[0093] The silicon-based anode and its preparation method provided in this disclosure have the following advantages compared with related technologies:

[0094] The method for preparing the silicon-based anode provided in this embodiment includes: obtaining a covalent organic framework material precursor; mixing the covalent organic framework material precursor with silicon nanosheets to obtain a mixed solution; heat-treating the mixed solution to cause the covalent organic framework material precursor to undergo a polymerization reaction to generate a covalent organic framework material buffer layer, and attaching the covalent organic framework material buffer layer to at least a portion of the surface of the silicon nanosheets to obtain a silicon-based anode. The covalent organic framework (COB) buffer layer exhibits high chemical stability and elasticity. Under pressure, the polymer chains in the COB buffer layer do not break, and the buffer layer returns to its original shape after the pressure is removed. By combining a COB precursor with silicon nanosheets through heat treatment, a silicon-based anode with a COB buffer layer on the surface of the silicon nanosheets is obtained. This means that the silicon nanosheets have a COB buffer layer on their surface. When the silicon nanosheets expand, the COB buffer layer expands slightly along with them, but not as much as the expansion rate of the silicon nanosheets themselves. Thus, the COB buffer layer provides a certain degree of constraint on the silicon nanosheets. When the silicon nanosheets contract, the COB buffer layer also contracts and returns to its original shape. Therefore, the strong confinement and buffering effect of the COB buffer layer can effectively suppress and buffer the large volume changes caused by the silicon nanosheets during charging and discharging, thereby reducing the expansion rate of the silicon-based anode.

[0095] One or more technical solutions in the embodiments of this disclosure have at least the following technical effects or advantages:

[0096] (1) In solid-state batteries, the covalent organic framework material buffer layer has high chemical stability and large elasticity. Its strong constraint buffering effect can fully suppress and buffer the huge volume change caused by silicon nanosheets during charging and discharging, thereby reducing the consumption of electrolyte and forming a uniform, stable and strong SEI layer, thereby improving the long cycle and rate performance of solid-state batteries.

[0097] (2) Covalent organic framework materials do not contain any metal elements, and the raw materials used for synthesis are all common organic raw materials, which have the characteristics of wide availability, no pollution and low cost.

[0098] (3) In solid-state batteries, the covalent organic framework material buffer layer has certain lithium storage performance and will not significantly reduce the battery capacity of solid-state batteries.

[0099] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a silicon-based anode, comprising: A precursor for a covalent organic framework material was obtained; The covalent organic framework material precursor is first mixed with silicon nanosheets to obtain a mixed solution; as well as, The mixed solution is heat-treated to cause the covalent organic framework material precursor to undergo a polymerization reaction, generating a covalent organic framework material buffer layer, and the covalent organic framework material buffer layer is attached to at least a portion of the surface of the silicon nanosheet to obtain a silicon-based anode.

2. The method of claim 1, wherein, The obtained covalent organic framework material precursor includes: Tris(4-aminophenyl)amine, diacid monomer, and solvent were mixed in a second step to obtain a precursor for a covalent organic framework material.

3. The method of claim 2, wherein, The dihydride monomer includes at least one of the following: Pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, and perylenetetracarboxylic dianhydride.

4. The method of claim 2, wherein, The tri(4-aminophenyl)amine and the binary The molar ratio of anhydride monomers is (3:2) to (4:2).

5. The method of claim 2, wherein, The solvent is an amide solvent.

6. The method of any one of claims 2 to 5, wherein, The volume of the solvent is 150 mL to 250 mL relative to 1 mol of the diacid monomer.

7. The method of claim 2, wherein, The molar ratio of silicon atoms to the diacid monomer in the silicon nanosheet is (20:1) to (40:1).

8. The method according to any one of claims 1 to 5, wherein, The process parameters for the heat treatment include: The heating temperature is 120℃~180℃, and the heating time is 56 h~80 h.

9. A silicon-based anode prepared by the method according to any one of claims 1 to 8.

10. A battery comprising the silicon-based negative electrode of claim 9.

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